The present invention relates to a double beam spectrophotometer which has two routes of optical paths for a sample side beam and a reference side beam.
FIG. 2 shows a schematic view showing an example of an optical path structure in a general double beam spectrophotometer which has been known conventionally. The spectrophotometer is provided for measuring an absorbance or transmittance of, for example, a liquid sample contained in a sample cell.
In FIG. 2, light irradiated from a light source 1 is introduced into a monochromator 2, wherein monochromatic light having a predetermined wavelength is taken out. The monochromatic light is sent to a sector mirror 4 by a reflecting mirror 3, and is alternately distributed by the sector mirror 4, which rotates on an axis A, into two directions, that is, a sample side and a reference side. In a standard sample chamber 11, there are provided a reference side cell 12 containing only a solvent or liquid, and a sample side cell 13 containing a sample solution. A reference side beam R reflected by the sector mirror 4 is irradiated to the reference side cell 12 through a reflecting mirror 5, and after the reference side beam R passes through the reference side cell 12, the beam is reflected and condensed by a condensing mirror 7 to be guided to a light receiving surface of a photodetector 10.
On the other hand, a sample side beam S which does not hit a reflecting mirror surface of the sector mirror 4 is irradiated to the sample side cell 13 through a reflecting mirror 6, and after the sample side beam S passes through the sample side cell 13, the beam is reflected and condensed by a condensing mirror 8, and further returned and reflected by a plane mirror 9 to be guided to the light receiving surface of the photodetector 10. Since the reference side transmitted beam Rxe2x80x2 which has passed through the reference side cell 12, and the sample side transmitted beam Sxe2x80x2 which has passed through the sample side cell 13, are guided alternately into the photodetector 10 in synchronism with a rotation of the sector mirror 4, the absorbance can be calculated by using a strength difference or strength ratio between the light receiving signals of both beams.
In the double beam spectrophotometer described above, since it is preferable to keep the symmetry between the sample side beam S and the reference side beam R as much as possible, optical paths of both beams S and R are normally set to be parallel to each other on the same horizontal plane. Also, in order to commonly use an accessary device, such as a sample chamber, with respect to various kinds of spectrophotometers sold by the same maker or manufacturer in a market, in the same maker, a clearance or separated distance d (normally around 100 mm to 200 mm) between the beams S and R is unified or standardized in many cases.
In the conventional optical path structure as described above, there is no problem in case the liquid sample accommodated in the sample cell with the predetermined size is measured. However, in case a solid sample, especially, a large-sized solid sample is measured, a clearance or separated distance d between the sample side beam S and the reference side beam R becomes a cause for limiting the size of the sample. Namely, a part of the large sample has to be cut into a measurable size. It is impossible to measure the large-sized sample which can not be cut as described above. In recent years, a size of a silicon wafer for a semiconductor or liquid crystal display plate, which is one of objects to be measured by the spectrophotometer of this type, has become larger rapidly, and the number of cases is increasing where the measurement can not be carried out in the standard sample chamber in which the separated distance d is set generally as described above.
Also, in the aforementioned conventional structure, since the beam passes through the sample in the horizontal direction, in order to set a sample with a thin shape, such as a silicon wafer or liquid crystal display plate, in the sample chamber, a holding mechanism for holding a sample vertically is necessary. This kind of the holding mechanism requires a cost, and setting thereof takes time and labor. Accordingly, in case the solid sample is measured, it is preferable to have a structure in which the sample can be placed horizontally.
The present invention has been made to solve the aforementioned problems, and an object of the invention is to provide a double beam spectrophotometer which can measure a solid sample with a large size in the condition that the sample is placed horizontally.
Further objects and advantages of the invention will be apparent from the following description of the invention.
To achieve the aforementioned object, the present invention provides a double beam spectrophotometer using a sample side beam and a reference side beam, wherein the sample side beam is provided or irradiated from a lower surface or upper surface of the sample, and the sample side beam passing through or ejected from the upper surface or the lower surface of the sample is reflected by a reflection optical system to be guided to a detector disposed outside projecting surfaces in a vertical direction of the sample. Also, in the double beam spectrophotometer, the reference side beam advancing parallel to the sample side beam is reflected by a reflection optical system having one or plural reflecting surfaces such that the reference side beam passes around the sample, and the reference side beam is guided to the detector.
Namely, in this structure, the sample side beam and the reference side beam advance in a direction to respectively hit the lower surface or the upper surface of the sample. The sample side beam advances straight as it is to pass through the sample. On the other hand, the reference side beam is deflected right before the sample by the reflection optical system in the direction to perpendicularly or obliquely cross the sample side beam, and reaches the detector without hitting the sample.
Also, in the double beam spectrophotometer according to the invention, reflecting mirrors, which can be freely retreated, may be inserted in optical paths for the sample side beam and the reference side beam so that both beams are deflected, and also, another reflection optical system may be inserted if necessary. Then, both beams may be guided into a sample chamber on a premise that the sample side beam and the reference side beam are disposed parallel to each other on the same horizontal plane with a predetermined distance therebetween.